adder.accept(accumulator, SomeEnum.B);
    ImmutableSet<SomeEnum> set = collector.finisher().apply(accumulator);
    assertThat(set).containsExactly(SomeEnum.A, SomeEnum.B);

    // Subsequent manual manipulation of the accumulator must not affect the state of the built set
    adder.accept(accumulator, SomeEnum.C);
    assertThat(set).containsExactly(SomeEnum.A, SomeEnum.B);
  }

  @J2ktIncompatible

    ImmutableSet<E> toImmutableSet() {
      if (set == null) {
        return ImmutableSet.of();
      }
      ImmutableSet<E> ret = ImmutableEnumSet.asImmutable(set);
      set = null; // subsequent manual manipulation of the accumulator mustn't affect ret
      return ret;
    }
  }

  @GwtIncompatible
  @SuppressWarnings({"rawtypes", "unchecked"})
  static <E extends Comparable<? super E>>

import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.util.Iterator;
import java.util.Set;
import javax.annotation.CheckForNull;

/**
 * An interface for representing and manipulating an origin node's adjacent nodes and edge values in
 * a {@link Graph}.
 *
 * @author James Sexton
 * @param <N> Node parameter type
 * @param <V> Value parameter type
 */
@ElementTypesAreNonnullByDefault

    ImmutableSet<E> toImmutableSet() {
      if (set == null) {
        return ImmutableSet.of();
      }
      ImmutableSet<E> ret = ImmutableEnumSet.asImmutable(set);
      set = null; // subsequent manual manipulation of the accumulator mustn't affect ret
      return ret;
    }
  }

  @GwtIncompatible
  @SuppressWarnings({"rawtypes", "unchecked"})
  static <E extends Comparable<? super E>>

 */

package com.google.common.graph;

import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.util.Set;
import javax.annotation.CheckForNull;

/**
 * An interface for representing and manipulating an origin node's adjacent nodes and incident edges
 * in a {@link Network}.
 *
 * @author James Sexton
 * @param <N> Node parameter type
 * @param <E> Edge parameter type
 */
@ElementTypesAreNonnullByDefault